1. Field of the Invention
The present invention relates to a method of manufacturing displays, adapted to form a contact hole in an insulating film, which is formed on a surface of an insulating substrate constituting a display, by an etching operation, and an apparatus for manufacturing displays.
2. Description of the Related Art
A method of manufacturing a display has a step of forming a gate electrode wire and a gate electrode on a surface of an insulating substrate, such as a glass substrate, a step of thereafter forming a gate insulating film and a semiconductor layer, and a step of thereafter forming a source electrode wire, a source electrode and a drain electrode to complete a TFT (thin film transistor). A passivation film made of a silicon nitride film and the like is then formed so as to protect the TFT. An inter-layer insulating film made of a transparent resin is then formed, and a contact hole is formed in the passivation film and inter-layer insulating film. Finally, a picture element electrode is formed on the inter-layer film to obtain a TFT array. The picture element electrode is electrically connected to the drain electrode via the contact hole made in the passivation film and inter-layer insulating film.
However, the following problems occur during the step of forming the contact hole in the insulating film. In a contact hole forming step in a related art method of this kind, a so-called dry etching method was generally used in which a voltage was applied between a pair of electrodes to generate an electric field therebetween, and plasma was thereby generated on an insulating substrate to be etched provided on one of the electrodes to thereby carry out a reactive ion etching operation. In order to form a contact hole in an insulating film, such as a silicon nitride film and a silicon oxide film, a fluorine-containing etching gas capable of carrying out a stable, high-accuracy etching operation is generally used. An electrode material for a dry etching unit is generally made of an aluminum alloy as a base material in many cases for the reasons that the aluminum alloy is inexpensive, highly processable, small in weight, and capable of forming alumite on a surface due to the anodic oxidation. In order to improve the uniformity of the etching operation, the electrodes are formed larger than the insulating substrate to be etched.
When an etching operation for forming a contact hole is carried out in an apparatus for manufacturing displays, adapted to carry out such a dry etching operation, a surface of a lower electrode not having insulating substrate mounted thereon and in a non-sheltered state (projected) is exposed to plasma, and an aluminum component of the electrode and fluorine contained in the etching gas react with each other. As a result, nonvolatile reaction product, such as nonvolatile aluminum fluoride is generated and deposited on the surface of the insulating substrate and surroundings. When this nonvolatile reaction product is deposited during the etching operation on the passivation film on a side surface of the contact hole of the insulating substrate, an exposed metal film on a bottom surface of the contact hole, or an inter-layer insulating film, the nonvolatile reaction product forms a mask for the etching operation, so that a rough surface (irregular portion) occurs. When the surface becomes rough, imperfect coverage occurs during the formation of a picture element electrode to cause the breaking of wires and imperfect display of an image to occur.
FIGS. 7A to 7D are sectional views showing a contact hole forming step in a related art display. Referring to FIGS. 7A to 7D, a gate wire 15 is formed on an insulating substrate 3, and then a first insulating film 16, which constitutes a gate insulting film, so as to cover the gate wire. A source wire 17 is then formed on the first insulating film 16. A second insulating film 18 turning into a passivation film is formed, and then an interlayer insulating film 19 made of a transparent resin is formed. FIG. 7A is a sectional view of a display material not yet subjected to an etching operation for forming a contact hole, FIG. 7B is a sectional view of the display material being etched, FIG. 7C is a sectional view of the display material the etching of which is completed, and FIG. 7D is a sectional view of the display material which has been processed with a wet chemical. As shown in FIGS. 7A to 7D, minute recesses and projections 21 are formed on the surfaces of the inter-layer insulating film 19, second insulating film 18 and source wire 17, and those of the inter-layer insulating film 19, second insulating film 18, first insulating film 16 and gate wire 15 due to a nonvolatile reaction product 20 of the aluminum fluoride and the like of the electrode scattered during the etching operation. In such condition, the breaking of a wire occurs due to imperfect coverage when a picture element electrode is formed in a subsequent step. In order to solve these problems, it is necessary to improve the uniformity of the etching operation and prevent the deposition of the nonvolatile reaction product.
In order to solve these problems, a method and an apparatus for manufacturing an insulating substrate constituting a related art display include a reactive ion etching method adapted to generate an electric field between a pair of electrodes by applying a voltage therebetween, and thereby generate plasma on an insulating substrate to be etched provided on one of the electrodes, wherein an insulator covering a surface as a whole of the substrate-side electrode is provided on the same electrode, the insulating substrate being provided in a recess formed in a surface of this insulator so that the surface of the insulating substrate becomes flush with that of the insulator, an etching rate being thereby set uniform over the whole region of the surface of the insulating substrate constituting an etching sample, the deposition of reaction product on the insulating substrate being prevented (refer to, for example, JP-A-5-129242 (FIG. 1)).
However, in the above-described related art method and apparatus for manufacturing displays, an insulator is provided on a substrate-provided side electrode so that this electrode as a whole is covered therewith, and the insulating substrate is provided in a recess formed in a surface of this insulator so that the surface of the substrate is flush with that of the insulator. Therefore, it is necessary that the recess having a height equal to the thickness of the insulating substrate and capable of housing the insulating substrate therein be formed. This causes the forming of the insulator to become troublesome. When etching operations are carried out repeatedly, the surface of the insulator set flush with that of the substrate is also etched to cause the surface of the insulator to become lower than that of the substrate. Thus, it is difficult to maintain a uniform etching rate.